In general, a spherical bearing is installed between an upper structure of a bridge and a pier and delivers the weight from the upper structure to the pier, and also is installed widely in bridges which need functions of allowing the thermal expansion or contractions of the upper structure, supporting the dynamic weight when a car or a train starts or brakes, absorbing shock when an earthquake breaks out, and preventing the dislocation of the upper structure by a negative reaction, for example, a railroad bridge. Such a spherical bearing is going to be explained referring to FIG. 1.
FIG. 1 is a cross-sectional view showing an exemplary spherical bearing in a prior art.
The spherical bearing (10) shown in FIG. 1 is a supporting device, which is installed between an upper structure such as the superstructure of a bridge and a lower structure such as a pier and supports the upper structure on the lower structure. Such a spherical bearing (10) is used to support the upper structure safely while allowing up-and-down rotation of the upper structure, that is, tilting of the upper structure due to the difference in distribution of vertical weight to the front, rear, right, and left with a supporting point as a center when the dynamic weight when a regular vehicle or a train starts or brakes or an earthquake acts, and according to the usage of the spherical bearing allowing the upper structure to slide in a direction or both directions with respect to the lower structure through the thermal expansion or a horizontal load caused by starting or braking of the regular vehicle or train.
As shown in FIG. 1, a conventional spherical bearing (10) comprises a spherical block (20) having a partial shape of a sphere, a spherical groove member (30) formed in a spherical groove (31), and a weight-delivering member (40) for delivering the weight of an upper structure supported on the top to the spherical block (20) and sliding with respect to the spherical block (20).
The spherical block (20) includes a convex spherical surface (21) formed convexly downward, on the top surface is formed a slider-installing groove (22), and in the slider-installing groove (22) is installed a slider (23) such as PTFE. And on the surface of the convex spherical surface (21) is formed a chrome-plating layer (24).
In the lower portion of the spherical block (20) is installed the spherical groove member (30) made of metal. In this embodiment, the spherical groove member (30) is fixed on a lower structure such as a pier supporting the weight of the upper structure, and formed with a spherical groove (31) having a shape corresponding to the convex spherical surface (21) on the top surface therefore. In the spherical groove (31) is formed a slider-installing groove (32) along the surface thereof, in which the slider-installing groove (32) has a spherical shape and there is installed a slider (33) such as the PTFE that is curved spherically.
On the top side of the spherical block (20) is installed the weight-delivering member (40) made of metal. This weight-delivering member (40) has a flat bottom surface (41). On the bottom surface (41) of the weight-delivering member (40) is attached a stainless-steel plate (42).
The conventional spherical bearing (10) as in the above is very hard to manufacture since it must form slider-installing grooves (22, 32) for installing the sliders (23, 33) in the spherical groove member (30) and needs the slider (33) having a spherical shape.
In general, as shown in FIG. 1, for the spherical block (20) of a spherical base having the slider (33) such as PTFE on both top and bottom thereof, what is made of regular steel is used widely. Such a spherical type is used widely in Europe.
In cases, for the spherical block (20), what is made of high-strength brass may be used. In this case, a groove is formed on a surface of the spherical block (20) and a solid lubricant, graphite, is filled in the groove, reducing friction.
The brass has an excellent anti-abrasiveness, but since it is much more expensive than regular bearing material the traditional spherical bearing (10) using the brass spherical block (20) is very expensive.
Also, the brass spherical block (20) made of brass has a shortcoming that in some period after installation it gets stuck with the spherical groove member (30) or the weight-delivering member (40), failing to function as a spherical bearing.
The brass spherical block (20) made of brass is hard to manufacture because it must have grooves formed on the surface of the spherical block (20) for injecting graphite and the like.
Besides, the conventional spherical bearing (10) is heavy because the spherical block (20), the spherical groove member (30), and the weight-delivering member (40) must be all made of metal, and very hard to manufacture because the spherical block (20) must be made by melting the steel or brass in a high temperature and casting.